Field of the Invention
The invention relates to a semiconductor component with a high-voltage endurance edge structure. The semiconductor component is formed of a semiconductor body having a first surface and an end region. At least one inner zone of a first conductivity type is disposed in the semiconductor body and borders at least partially on the first surface of the semiconductor body. At least one drain zone borders on the at least one inner zone. Base zones of a second conductivity type are embedded in the semiconductor body along the first surface and source zones of the first conductivity type are embedded in the base zones.
Such semiconductor components can be constructed, for example, as MOSFETs if the drain zone bordering on the inner zone has the same conductivity type as the inner zone. On the other hand, such semiconductor components which can be controlled by the field effect, are also known as IGBTs to the extent that the drain zone is constructed as an anode zone with a conductivity type opposite to that of the inner zone. A semiconductor component, in which a multiplicity of parallel-connected individual components respectively disposed in cells are disposed tightly packed in a cell array is disclosed in U.S. Pat. No. 5,008,725.
In a freewheeling operation, the flooding of the semiconductor substrate with charge carriers of both polarities typically occurs with such semiconductor components. The charge carriers are distributed over the entire inner zone, the charge carriers particularly also diffuse out laterally in the edge region over the active cell array. During subsequent commutation of the inner zone of the semiconductor component, the charge carriers of the one conductivity type flow off uncritically via the large-area drain metallization on the rear of the wafer. While the charge carriers of the respective other conductivity type flow off via the respective base zones and the source electrode on the front of the wafer. The cells disposed in the immediate edge region of the cell array are severely stressed because of the very high reverse flow density there. Depending on the commutation gradient, the cells can be destroyed even in the case of relatively weak reverse flows as a consequence of the switching on of the parasitic bipolar transistors that are present in principle in the case of such a semiconductor component.
Moreover, the undesired voltage breakdowns also occur specifically in avalanche operation. Here, the electric field in the edge region is particularly high, as a consequence of the curvature, caused by the edge, of the doping regions and thus of the asymmetric characteristic of the equipotential lines. Because of the asymmetric field distribution in the edge region, it is possible here even for weak currents to lead to the destruction of the semiconductor component.
In order to avoid such undesired voltage breakdowns, in the case of the semiconductor component of the generic type, annular doping regions are disposed in the edge region outside the active cells. Such protective rings, by which local field strength peaks are to be reduced in the edge region, are known for example, from Canadian Patent No. 667,423. The protective rings described there are floating, that is to say they have no defined potential. It is known that such floating protective rings must have wide dimensions towards the edge, since the electric field strength in the protective rings is reduced to virtually zero.
It is, moreover, possible to connect the protective rings to the source metallization via contact holes. In this case, the non-floating protective rings are at the same potential as the source zone. The production of the floating and non-floating protective rings is, however, extremely complicated and thus very cost intensive, particularly in the case of a self-adjusting technology. The particular problem in the production of the protective rings in a self-adjusting technology resides in the case, in particular, in the avoidance of a short circuit between the source electrode and the gate electrode.
Such protective rings are typically produced by ion implantation. It is known that in ion implantation the semiconductor crystal or its surface is severely disturbed in such a way that the crystal is not optimally recrystallized even in a subsequent repair step. During the subsequent growth of the gate oxide, to the quality of which particularly high requirements are placed, interface charges can be produced at the interface with the semiconductor body and/or moveable or fixed charges can be produced in the gate oxide. The parasitic charges lead to undefined component capacitances in the gate oxide, making it difficult for the semiconductor component to be switched in a defined fashion in this region.